Ok I just noticed this in the 4 for 3 section and it's a pretty good deal if you are missing a good few, or just starting to collect.
Series 1,2,3,8 are £7.98 each
Series 4 is £8.48
Series 5,6,7 are £8.97 each
If you mix them up you can get the lot for £50.85 (£6.36 each), or if you are lucky and just need 1,2,3,8 they come in under £6 each.
Or you can dig around and find some other good buys for around the same price to maximise savings (e.g. Party Of Five Season 1 for £8.97).